User collections of digital products are sometimes organized in libraries. Some examples of such libraries include iTunes® music libraries (mark of Apple Computer, Inc.). Some additional examples include other libraries whose entry selection and/or modification is or could be digitally tracked, such as other iTunes libraries (e.g., movies, TV shows, podcasts, apps, ringtones, and radio stations), and other libraries containing entries such as songs, videos, games, podcasts, and/or digitally-presented products. Sometimes a library is maintained in conjunction with user activity on sites such as the iTunes store, Last dot fm, Pandora dot com, YouTube dot com, Hula dot com, Amazon dot com, and their respective competing or complementary sites, and in connection with recording systems such as the Tivo system, Comcast On Demand system, etc. (marks of their respective owners). Song plays, game rentals, videos, audio library checkouts, podcasts, online magazines, and other digital goods may be entries in some libraries of user-selected (and/or user-accepted) digital goods. Web analytics, purchasing histories, and other mechanisms used to track user browsing and/or user purchases may also be used to identify library entries.